This invention relates to a method and apparatus for masking logical unit numbers in a shared data storage system.
A data storage system typically consists of an array of disk units and one or more storage controllers. The disks may be accessed using the well-known SCSI protocol, over a Fibre Channel (FC) connection. Within a SCSI storage system, groups of disks are bound into logical storage units, each of which is assigned a logical unit number (LUN). Under SCSI, a storage unit is addressed by a SCSI target address, which selects a particular storage controller, and by the LUN, which selects one of the storage units connected to that controller. For a stand-alone disk, the LUN is always zero.
Such a storage system may be shared between two or more processing nodes, possibly running under different operating systems. In such a case, it is necessary to provide some form of LUN masking, to ensure that each node can access only its own LUNs, and cannot access LUNs belonging to another node.
There are two approaches currently being taken to LUN masking. In a first approach, LUN masking is performed within each storage controller, using the Worldwide Name (WWN) of the FC Host Bus Adapter (HBA) of each processing node to map LUNs on to the nodes. In a second approach, LUN masking is performed within each processing node, using the unique WWN of the storage controller. Masked LUNs are hidden from the operating system.
Both of these known LUN masking techniques require special software, running either within the storage system, or in the processing nodes. Such software is generally expensive.
The object of the invention is to provide a novel solution to the problem of LUN masking, which is less expensive than known solutions.
According to the invention a method of masking logical unit numbers comprises the steps:
storing a maximum LUN value in non-volatile storage in a first processing node;
storing a start LUN value in non-volatile storage in a second processing node;
causing the first processing node to perform, on boot-up, a device discovery procedure in which it scans a shared data storage system to find storage units with LUNs not greater than the maximum LUN value; and
causing the second processing node to perform, on boot-up, a device discovery procedure in which it scans the shared data storage system to find storage units with LUNs not less than the start LUN value.
It will be shown that the invention allows LUN masking to be achieved relatively inexpensively with only minimal modification to the operating systems of the processing nodes, using existing device discovery features of the operating system.